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Darwin’s Theory of Evolution

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1 Darwin’s Theory of Evolution
Chapter 16 Darwin’s Theory of Evolution

2 Chapter 16 Mystery SUCH VARIED HONEYCREEPERS Page 449…
Hypothesis: How did all these birds get to Hawaii? How did some of them come to have such specialized diets?

3 Section 16.1 Darwin’s Voyage of Discovery
Objectives: What was Charles Darwin’s contribution to science? What three patterns of biodiversity did Darwin note? Define: Evolution Fossil

4 I. Darwin’s Epic Journey
Charles Darwin – England – 1809 Evolution – process of change over time Darwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors 1831 – HMS Beagle – 5 year voyage – map coastline of SA Darwin planned to collect specimens of plants and animals Darwin’s work = vital insights into today’s world by showing how living world is constantly changing  helps us understand modern phenomena (drug-resistant bacteria & newly emerging diseases like avian flu)

5 II. Observations Aboard the Beagle
1 day – Brazilian forest = 68 species of beetles (when he wasn’t particularly looking for beetles) Observed characteristics & habits Kept eyes and mind open to larger patterns into which observations might fit 3 distinct patterns: Species vary globally Species vary locally Species vary over time

6 A. Species Vary Globally
SA, Australia, Africa Darwin noticed that different, yet ecologically similar, animal species inhabited separated, but ecologically similar habitats around the globe. Rhea – flightless, ground-dwelling bird  SA Ostrich – same characteristics  Africa Emu – same characteristics  Australia Rabbits in Eur. grasslands, but not in SA Kangaroos only in Aus.

7 B. Species Vary Locally Darwin noticed that different, yet related, animal species often occupied different habitats within a local area 2 species of rhea (SA) – 1 in grassland & 1 in colder, harsher scrubland Galapagos Islands – close to each other but different ecological conditions Distinct forms of giant land tortoises (shells varied from one island to another) Different islands = different varieties of mockingbirds (all resembled mockingbirds in SA)  beaks w/ different shapes (wrens, warblers, blackbirds)

8 Mystery Clue Page 452… Like the small brown birds on the Galapagos, Hawaiian honey creepers live on islands with slightly different habitats. How might these varied habitats have affected the evolution of honeycreeper species

9 C. Species Vary Over Time
Darwin also collected fossils Fossil – preserved remains or traces of ancient organisms Some looked like current living organisms, but some looked nothing like current living organisms Darwin noticed that some fossils of extinct animals were similar to living species Glyptodont – giant armored animal  found in area where current armadillo is found Armadillo = smaller version of glyptodont

10 D. Putting the Pieces of the Puzzle Together
Mockingbirds = 3 species of finches found nowhere else Wren, warbler, blackbirds = all species of finches found nowhere else Tortoises, marine iguanas, plants = only on Galapogos Did these species evolve from SA species? Suggested: species are not fixed & can change by some natural process

11 Section 16.2 Ideas that Shaped Darwin’s Theory
Objectives: What did Hutton and Lyell conclude about Earth’s history? How did Lamarck propose that species evolve? What was Malthus’s view of population growth? How is inherited variation used in artificial selection? Define: Artificial selection

12 I. An Ancient, Changing Earth
People thought: Earth was few 1000 yrs old & didn’t change much Hutton and Lyell concluded that the Earth is extremely old and that the processes that changed Earth in the past are the same processes that operate in the present 1785 – Hutton presented info Lyell – built on Hutton – Principles of Geology

13 A. Hutton and Geological Change
Recognized connections b/w geological processes and geological features (mountains, valleys, folded layers of rock) Some rocks form from lava & some form from layers of sediment Proposed force beneath surface can push rock layers upward = mountain ranges Worn down by rain, wind, heat & cold Processes = v. slow so Earth must be much older Deep time – idea that our planet’s history stretches back over a period of time so long that it is difficult to imagine

14 B. Lyell’s Principles of Geology
Laws of nature = constant over time Uniformitarianism – geological processes we see today must be same ones that shaped Earth mya Ancient volcanoes released gases & lava Ancient rivers dug channels (canyons & valleys) Darwin uses Lyell’s insights Earthquake raised shoreline 3m out of sea Could be how Andes mountains formed Explains how fossils of marine animals could be found at tops of mountains

15 II. Lamarck’s Evolutionary Hypothesis
Jean Baptiste Lamarck – proposed theory of evolution based on growing fossil record Lamarck suggested that organisms could change during their lifetimes by selectively using or not using various parts of their bodies. He also suggested that individuals could pass these acquired traits onto offspring, enabling species to change over time Published ideas in 1809 – year Darwin was born

16 A. Lamarck’s Ideas Proposed all organisms have inborn urge to become more complex and perfect As a result  organisms change and acquire features that help them live more successfully in environments Orgs. can change size/shape of organs by using bodies in new ways Example: waterbird = long legs Structures of orgs. could change if not used Example: bird stopped using wings = smaller wings Acquired characteristics – traits altered by an org during its life Inheritance of acquired characteristics – traits acquired during lifetime can be passed on to offspring

17 B. Evaluating Lamarck’s Hypothesis
Lamarck was Incorrect b/c: Orgs do not have inborn drive to be perfect Evolution does not mean that over time species becomes “better” somehow Evolution does not progress in predetermined direction traits acquired by orgs during lifetime cannot be passed on to offspring Lamarck was one of 1st to try to explain evolution scientifically using natural processes Recognized link b/w org’s environment and body structures

18 III. Population Growth 1798 – Thomas Malthus – humans were being born faster than they were dying = overcrowding Malthus reasoned that if human population grew unchecked, there wouldn’t be enough living space and food for everyone Forces that work against pop growth = war, famine, disease Darwin applied to other orgs (maple tree, oyster) Darwin realized most organisms don’t survive and reproduce…  wondered which individuals survived and why

19 IV. Artificial Selection
Darwin studied change produced by plant and animal breeders Breeders knew that indiv. orgs. vary: some bear larger/smaller fruit than other species & some cows bear more/less milk than others in same herd Told Darwin that some of this variation could be passed from parent to offspring (used to improve crops/livestock) Artificial selection – nature provides the variation and humans select those they find useful & allow them to reproduce to produce offspring with similar traits Darwin  recognized natural variation was v. impt b/c provided raw material for evolution

20 Section 16.3 Darwin Presents His Case
Objectives: Under what conditions does natural selection occur? What does Darwin’s mechanism for evolution suggest about living and extinct species? Define: Adaptation Fitness Natural selection

21 I. Evolution by Natural Selection
Evolution is a Scientific mechanism On the Origin of Species Combined ideas of his own with Lamarck and Malthus

22 A. Struggle for Existence
If more individuals are produced than can survive  members of a population must compete to obtain food, living space, and other limited necessities of life Called: Struggle for Existence Which individuals come out on top of struggle?

23 B. Variation and Adaptation
Individuals have natural variations among heritable traits Some variants are better suited to life in their environment than others Predatory species that are faster, longer claws, sharper teeth  catch more prey Prey species that are faster, better camouflaged  avoid being caught Adaptation – any heritable characteristic that increases an org’s ability to survive and reproduce in its environment Body parts or structures (tiger’s claws, camouflage) Physiological functions (photosynthesis) Behaviors (complex avoidance strategies of prey)

24 C. Survival of the Fittest
Differences in adaptations affect an indiv’s fitness Fitness – how well an org can survive and reproduce in its environment High fitness – well suited to env; can survive & reproduce Low fitness – not well suited to env die w/o reproducing or leave few offspring Survival of the fittest – difference in rates of survival and reproduction Survival – means more than living; must also reproduce and pass on adaptations to next generation

25 D. Natural Selection Natural selection – mechanism for evolution - process by which orgs w/ variations most suited to local env survive and leave more offspring Only certain indivs in population produce new indivs Fitness determined by environment Natural selection occurs in any situation in which more individuals are born than can survive (struggle for existence), there is natural heritable variation (variation and adaptation), and there is variable fitness among indivs (survival of fittest). Well adapted indivs survive and reproduce Populations continue to change as they become better adapted or as env changes Natural selection acts only on inherited traits b/c those are the only chars that parents can pass onto offspring

26 Natural selection does not make orgs “better”
Adaptations don’t have to be perfect – just good enough to enable org to pass its genes to next generation doesn’t have to move in fixed direction – no one perfect way of doing something If local env changes  traits that were once adaptive may no longer be useful and different traits may become adaptive If env changes faster than species can adapt = extinct

27 Mystery Clue Page 463… How might natural selection explain the history of the Hawaiian honeycreepers?

28 II. Common Descent Natural selection depends on ability of orgs to reproduce Every org alive today is descended from parents who survived and reproduced Well-adapted indivs in species survived and reproduce  well adapted species survive over time Living species are descended with modification from common ancestors (descent with modification) Implies life has been on Earth for v. long time Hutton & Lyell – deep time gave enough time for natural selection to occur Used fossil record for evidence

29 “Tree Thinking” – implies that all organisms are related
Darwin based explanation for diversity of life on idea that species change over time “Tree Thinking” – implies that all organisms are related Common ancestor shared by tigers, panthers, cheetahs Common ancestor shared by these felines and horses, then bats Farther back  all mammals share ancestor with birds, alligators, fish According to the principle of common descent, all species – living and extinct – are descended from common ancestors

30 Section 16.4 Evidence of Evolution
Objectives: How does the geographic distribution of species today relate to their evolutionary history? How do fossils help to document the descent of modern species from ancient ancestors? What do homologous structures and similarities Define: Biogeography Homologous structure Analogous structure Vestigal structure

31 I. Biogeography Biogeography – study of where orgs live now and where they and their ancestors lived in the past Patterns in the distribution of living and fossil species tell us how modern orgs evolved from their ancestors Pattern in which closely related species differentiate in slightly different climates Pattern in which very distantly related species develop similarities in similar environments

32 A. Closely Related but Different
Biogeography of Galapagos species suggested that population on island evolved from mainland species Over time  natural selection on islands produced variations among populations Resulted in different but closely related island species Weevils Cotton Wasps Beetle Snakes Scorpion Finches

33 B. Distantly Related but Similar
Similar habitats around world often home to animals and plants that are only distantly related Similar ground-dwelling birds inhabit similar grasslands in Europe, Aus, Africa Differences in body structures among those animals provide evidence that they evolved from different ancestors Similarities among those animals provide evidence that similar selection pressures caused distantly related species to develop similar adaptations

34 Mystery Clue Page 465… How can biogeography help explain why some species of honeycreepers are found only on the Hawaiian Islands?

35 II. The Age of Earth and Fossils
2 potential difficulties age of Earth Gaps in fossil record

36 A. The Age of Earth 50 yrs after Darwin  physicists discovered radioactivity Geologists use radioactivity to establish age of certain rocks and fossils Radioactive dating indicates that Earth is ~4.5 billion years old This is plenty of time for natural selection to take place

37 B. Recent Fossil Finds “imperfection of geological record” – 1859 – paleontologists had not found enough fossils of intermediate forms of life to document evolution of modern species from their ancestors Many recently discovered fossils form series that trace evolution of modern species from extinct ancestors Since Darwin  paleontologists have discovered hundreds of fossils that document intermediate stages in evolution of many different groups of modern species Whales from ancient land mammals Dinosaurs & birds Fish & four-legged land animals

38 II. Comparing Anatomy and Embryology
All vertebrate limbs have same basic bone structure Some were used for crawling, some for climbing, some for running, others for flying

39 A. Homologous Structures
Darwin proposed animals w/ similar structures evolved from common ancestor w/ basic version of that structure Homologous structures – structures shared by related species and have been inherited from common ancestor Evolutionary theory explains existence of homologous structures adapted to different purposes as result of descent with modification from a common ancestor Biologists test whether structures are homologous by studying anatomical details, way structures develop in embryos, pattern in which they appeared over evolutionary history Similarities and differences among homologous structures help determine how recently species shared a common ancestor Common ancestor to all four-limbed animals = ancient lobe-finned fish (380 mya) Also some plants have homologous roots, stems, flowers

40 1. Analogous Structures Clue to common descent = common structure
Not common function Analogous structures – body parts that share common function but not structure Example: wing of bee and wing of bird

41 2. Vestigial Structures Vestigial structures – inherited from ancestors but have lost much or all of their original function due to different selection pressures acting on descendant Example: hipbones of bottlenose dolphin Presence does not affect organism’s fitness so natural selection does not act to eliminate it

42 B. Embryology Early developmental stages of many animals with backbones (vertebrates) look very similar Same groups of embryonic cells develop in same order and in similar patterns to produce many homologous tissues and organs in vertebrates Similar patterns of embryological development provide further evidence that organisms have descended from a common ancestor

43 III. Genetics and Molecular Biology
Darwin had no idea how heredity worked Some of most impt evidence for theory comes from genetics At molecular level, universal genetic code and homologous molecules provide evidence of common descent Also: we now understand how mutation and reshuffling of genes during sexual reproduction produce heritable variation on which natural selection operates

44 A. Life’s Common Genetic Code
All living cells use info coded in DNA and RNA to carry info from one generation to next and to direct protein synthesis Genetic code is nearly identical in almost all orgs (bacteria, yeasts, plants, fungi, animals) ALL ORGS EVOLVED FROM COMMON ANCESTORS THAT SHARED THIS CODE

45 B. Homologous Molecules
Homology not limited to physical structures Homologous proteins – share extensive structural and chemical similarities Example: cytochrome c – cellular respiration – found in almost all living cells Homologous genes – makes sense b/c all animals share same code Example: Hox genes – determine head-to-tail axis in embryonic development – found in almost all multicellular animals LIVING ORGS EVLOVED THROUGH DESCENT WITH MODIFICATION FROM A COMMON ANCESTOR

46 IV. Testing Natural Selection
To gather evidence  observe natural selection in progress Evolutionary change takes place over millions of years  tough to see change actually happening Some have been observed and studied in labs and controlled outdoor environments Bacteria, guppies Results support Darwin’s basic ideas Best examples of natural selection in action comes from observations on animals living in natural environment: Galapagos finches

47 A. A Testable Hypothesis
Galapagos finches – darwin thought they were wrens, warblers, and blackbireds b/c looked so different Once he learned all finches, he hypothesized: descended from common ancestor Beaks: different size and shapes – used to pick up and eat different foods  natural selection shaped beaks as became adapted to eat different foods

48 Peter and Rosemary Grant – Princeton
Darwin’s theory rested on 2 testable assumptions: For beak size and shape to evolve, there must be enough hertiable variation in those traits to provide raw material for natural selection Differences in beak size and shape must produce differences in fitness Caught and tagged each of one species on one island  recaught to see which lived and reproduced Each individual bird  recorded anatomical characteristics (wing length, leg length, total mass, beak length, beak depth, beak color, feather color) Showed great variation among finches

49 B. Natural Selection Individual finches w/ different-size beaks have better or worse chances of surviving both seasonal droughts and longer dry spells food scarce  birds w/ largest beaks – more likely to survive Result: average beak size in finch population has increased dramatically The Grants have documented that natural selection takes place in wild finch populations frequently, and sometimes rapidly Changes in food supply created selection pressure that caused finch populations to evolve w/in decades Occurred much faster than many researchers thought possible

50 Grants documented natural selection in nature
Their data also confirm that competition and environmental change drive natural selection Traits that don’t matter much under one set of environmental conditions became adaptive as environment changes during a drought The Grants’ work shows that variation within a species increases the likelihood of the species’ adapting to and surviving environmental change Without heritable variation in beak sizes, the medium ground finch would not be able to adapt to feeding on larger tougher seeds during a drought

51 C. Evaluating Evolutionary Theory
Advances in fields of biology & other sciences confirmed and expanded most of Darwin’s hypotheses Evolutionary theory – includes natural selection – offers insights that are vital to all branches of biology Evolution often called unifying theory of the life sciences Constantly reviewed as new data is gathered Debate questions (how new species arise and why species become extinct) Uncertainty about exactly how life began Questions remain about how evolution works; not whether evolution occurs To scientists, evolution is key to understanding natural world

52 Solve the Mystery Page 477….
Suppose a small group of birds, not unlike the modern honeycreepers, landed on one of Hawaii’s islands millions of years ago and then reproduced. Do you think all the descendants would have stayed on that one island? Explain. Do you think that the climate and other environmental conditions are exactly the same everywhere on the Hawaiian Islands? How might environmental conditions have affected the evolution of honeycreeper species? Explain how the different species of honeycreepers in Hawaii today might have evolved from one ancestral species. Why are islands often home to species that exist nowhere else on Earth?

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